This invention relates to an automatic focusing camera which, without a-priori knowledge of the distance of a subject to the camera, is capable of bringing the subject into focus in response to initiation of a camera cycle.
An automatic focusing camera is disclosed in U.S. patent application Ser. No. 729,289, filed Oct. 4, 1976, the disclosure of which is hereby incorporated by reference. In this camera, which is referred to hereafter as a camera of the type described, initiation of a camera cycle causes the lens mount of an adjustable lens assembly to be driven from a park position to a focus position dependent on subject distance as determined by a range finder system that generates a range parameter related to subject distance. When an exposure cycle in such a camera is initiated, the range finder system beams a burst of ultrasonic energy toward the subject. The interval of time between transmission of the burst and receipt of an echo is a parameter linearly related to subject distance by a fixed scale factor which defines a parametric relationship between time and the lens/subject function of the camera.
As is well known, the lens/subject function establishes the relationship between the distance of a subject and the position of the lens mount on the camera at which an image of the subject at that distance is in focus on the focal plane of the camera. Such function also establishes the range of distances over which subjects can be brought into focus by moving the lens mount.
Once the range parameter is generated, a motor moves the lens mount from a park position to a focus position depending on subject distance as determined by the range parameter, the shutter mechanism of the camera then being actuated to effect exposure of film located in a focal plane at a recording station behind the shutter mechanism. Sensing of the termination of exposure causes the motor to drive the lens mount back to its park position thereby terminating the exposure cycle.
When a photoelectrically controlled shutter mechanism is incorporated into a camera of the type described, it would appear that proper exposure as well as focus will be obtained each time an exposure cycle is initiated without a-priori knowledge of either light conditions of the scene being photographed or subject distance. This is not the case, however, when an attempt is made to photograph a subject located closer to the camera than the minimum distance designed into the optical system of the lens mount, or when an attempt is made to photograph a subject under flash illumination conditions and the subject is outside a predetermined range of distances dependent on the range of exposure values of the shutter mechanism and the light output of the flash unit. Under ambient lighting conditions, a poorly focused photograph will result when a subject is closer than a minimum distance. Under flash illumination conditions, an overexposed photograph will result when a subject is closer than the minimum predetermined range, and an underexposed photograph will result when the subject is further than the maximum predetermined range.
It is therefore an object of the present invention to provide a new and improved camera for controlling camera operation in accordance with subject distance.
A further object is to provide a camera capable of indication of operable limits of the camera versus subject distance under both ambient and flash mode conditions.